The prior art is characterized by the multilayer foil anodized electrode with a highly developed surface that is described in invention DE 102004011567, H05K 3/38, 2004, on whose current-carrying substrate, which is secured to a bearing film base suitable for roll processing, are applied layers of a valve metal and an oxide coating of bimodal morphology, with the fractal-like roughness of the interfaces preserved.
Adhesion of the layers being bonded is assured mainly not through chemical reaction of the components, but through the formation, at the interface, of a nanostructured transition region with a developed surface that consists of the material of the film base and that is vacuum-deposited from the vapor phase of another material, such as aluminum, a layer of which is the anode in this case.
A metal, preferably aluminum, is spray-coated onto the ion bombardment-activated rough surface of the base in a quasi-unified process in a reduced-pressure inert-gas atmosphere. When this is done, the nanostructure is formed as a differentiated mixture of the base material and the spray-coated metal, whose amount increases as the transitional nanolayer grows, reaching 100%, since the component of the base material accordingly smoothly decreases in volume, practically disappearing on the surface of this adhesive layer.
Thus, the base material in the nanocomposite adhesive layer formed, which has a thickness of from a few nanometers to several microns, gradually transitions to the spray-coated current-carrying metal, which ensures high strength of the bond between structural elements of the anode that have related bonding.
The nanocomposite transition region ensures the lyophobicity of the connection and serves as a barrier that prevents interdiffusion at the base-substrate interface.
The strength of the adhesive joint between the current-carrying layer and the polymer base can be increased by making a transition region in an orderly fashion by forming a diamond-like nanolayer of sp3-hybridization of amorphous carbon atoms (α-C:H) by the method of RU 2217394, C03C 17/34, G02B 5/28, 2003, which significantly improves the plastic properties of the transition region, providing elasticity to the multilayer material suitable for anode-fabrication roll technology.
Then the valve metal (preferably porous aluminum) is spray-coated by evaporation onto the surface of aluminum foil in a low-pressure inert-gas atmosphere in the presence of oxygen at a pressure 1-2 orders of magnitude lower. The working surface develops by the addition of material, not by its removal (as in conventional etching); the anode for electrolytic capacitors therefore is characterized by the use of a thinner foil as the current-carrying substrate.
Features of the dielectric oxide layer of this anode are its bimodal morphology, the dense uniform oxide discretely deposited on the developed substrate surface, and the porous oxide coating formed by electrolytic anodizing.
A shortcoming of the multilayer anode described is its unsatisfactory functional reliability due to migratory processes of interdiffusion in operation at the boundaries of autonomous inclusions of the valve metal with the materials of the adjacent substrate and oxide layers, which leads to instability of the basic technical characteristics of the electrolytic capacitor, significantly reducing its service life.
Said shortcoming is eliminated in the multilayer film anode for an electrolytic capacitor that is described in patent RU 56709, H01G 9/04, 2006, which for its technical essence and the number of its matching features has been chosen as the closest counterpart to the proposed anode.
The known multilayer anode for an electrolytic capacitor is characterized by broader engineering possibilities due to the use of different materials for the bearing film base, which are equally adapted to functional film coatings by means of an adhesive nanocomposite barrier layer.
Further, the anode has a higher specific capacitance and permittivity and, because of the high adhesive bond strength of the structural layers, also has improved mechanical properties and plasticity, which allows the multilayer anode to be fabricated by a roll process involving successive application to a film base of all coatings and layers in a quasi-unified process of ion-plasma spray-coating of materials from the vapor phase in the vacuum of a controlled atmosphere of an inert gas and a chemically active gas. This creates a general-purpose process, eliminates breaks in the flow, and lowers production costs.
Making inclusions of porous aluminum in the form of a conforming layer of an oxide coating similar to the developed substrate profile increases several-fold the contact surface of interaction with the electrolyte of the capacitor, which significantly increases its specific capacitance.
The valve metal in the form of a layer of a porous aluminum coating provides a developed open surface that is accessible for filling with electrolyte, which allows the use of solid electrolyte in the capacitor, thereby expanding the technological possibilities for using it as intended.
Process support with equipment for ion-plasma spray-coating of a valve metal with electrochemical activity ultimately is aimed as a result at creating a thicker layer of high-quality oxide to increase the working voltage of a higher-capacitance capacitor.
The bonding of the conforming layer of valve metal to the developed substrate surface by means of a heterojunction, which is a nanostructured composite consisting of the substrate material and spray-coated valve metal through diffusion driven by ions of an inert gas and a chemically active gas, makes possible expansion of the technological possibilities for making a film anode on almost any carrier by eliminating the sharp interfaces between the shaping layers.
However, a shortcoming of the known multilayer film anode, in which aluminum is used for the current-carrying substrate and the readily oxidized valve metal of the coating, consequently is the unstable geometry of the developed substrate surface that is formed, which reduces its practicality when used in an electrolytic capacitor.